1. Field of the Invention
The present invention relates to a telescopic boom for a vehicle or a hoist with a storage rack for at least two box girders guided displaceably in one another in the direction of their longitudinal axes, which are mounted to pivot about a horizontal pivot axle in the storage rack and which can be displaced reciprocally by means of a servo-drive.
2. Description of the Prior Art
Known telescopic booms of this type (DE 27 21 636 A1, DE 38 04 557 A1) have box girders guided in one another which can be displaced reciprocally along a straight line by means of a ram. The lower one of the box girders can be pivoted in a storage rack about a horizontal pivot axis and be pivoted with the bogie about a vertical axis, so that the load suspension arranged at the front end of the telescopic boom can be moved freely in a spatial area created by the possible pivot or swing angle and the extension length. If in the process the load suspension is arranged on a swivel head pivoting about a vertical axis, then in addition the load alignment can be selected independently of the respective pivot adjustment of the telescopic boom relative to the vertical axis of the storage rack. The design of the individual sections of the telescopic boom as box girders not only offers advantages with respect to the carrying capacity of the telescopic boom, but also with respect to arrangement of the servo-drive for extending and retracting the telescopic boom as well as to the placing of supply lines, because the servo-drive and the supply lines can be placed inside the box girders. This applies in particular for an embodiment (DE 27 21 636 A1) wherein the upper and the lower wall of the box girder, which is guided in the box girder on the storage rack side, exhibit longitudinal edge frames projecting over the box profile and guided on the box girder on the storage rack side, which with angled edge sections form takeup grooves for supply lines for hydraulic supply of rams of the load suspension. But the disadvantage of these known telescopic booms is that a linear, free passage for the telescopic arm has to be available between the point to be reached by the front end of the telescopic boom and the storage rack, which is, however, often not present, for example not if the telescopic boom is to be inserted into a space overhead through lateral openings. The higher such a lateral aperture lies above the storage rack, the more steeply therefore the telescopic arm has to be mounted about its horizontal pivot axis, the less the possible horizontal penetration width of the telescopic boom through the lateral opening becomes. To avoid this drawback the boom can be provided as a buckling arm with an articulated partitioning, though such buckling arm booms necessitate substantially higher structural and control expenses.